Hard landing?
I think the "hard landing" that passengers experienced onboard Flight 560 may have been what the industry calls a derotational accident, something that is not all that rare in a B767, and also including DC-10 and MD-11 aircraft (reference NTSB bulletin A-93-119).
Just how many hard landings (or should I say, derotational accidents), can one plane take before it shows visible damages and crumple on the tarmac? I do believe that this can happen MANY times without VISIBLE structural damages and therefore go unreported. Unreported accidents carry no history.
I hope someone with expertise in this topic can add their constructive comments on this.